concurrency, benchmark: read-committed STM isolation policy

clientv3/concurrency/stm.go

@@ -56,6 +56,12 @@ func NewSTMSerializable(ctx context.Context, c *v3.Client, apply func(STM) error
 	return runSTM(s, apply)
 }
 
+// NewSTMReadCommitted initiates a new read committed transaction.
+func NewSTMReadCommitted(ctx context.Context, c *v3.Client, apply func(STM) error) (*v3.TxnResponse, error) {
+	s := &stmReadCommitted{stm{client: c, ctx: ctx, getOpts: []v3.OpOption{v3.WithSerializable()}}}
+	return runSTM(s, apply)
+}
+
 type stmResponse struct {
 	resp *v3.TxnResponse
 	err  error
@@ -234,6 +240,14 @@ func (s *stmSerializable) commit() *v3.TxnResponse {
 	return nil
 }
 
+type stmReadCommitted struct{ stm }
+
+// commit always goes through when read committed
+func (s *stmReadCommitted) commit() *v3.TxnResponse {
+	s.rset = nil
+	return s.stm.commit()
+}
+
 func isKeyCurrent(k string, r *v3.GetResponse) v3.Cmp {
 	rev := r.Header.Revision + 1
 	if len(r.Kvs) != 0 {

tools/benchmark/cmd/stm.go

@@ -52,7 +52,7 @@ var (
 func init() {
 	RootCmd.AddCommand(stmCmd)
 
-	stmCmd.Flags().StringVar(&stmIsolation, "isolation", "r", "Repeatable Reads (r) or Serializable (s)")
+	stmCmd.Flags().StringVar(&stmIsolation, "isolation", "r", "Read Committed (c), Repeatable Reads (r), or Serializable (s)")
 	stmCmd.Flags().IntVar(&stmKeyCount, "keys", 1, "Total unique keys accessible by the benchmark")
 	stmCmd.Flags().IntVar(&stmTotal, "total", 10000, "Total number of completed STM transactions")
 	stmCmd.Flags().IntVar(&stmKeysPerTxn, "keys-per-txn", 1, "Number of keys to access per transaction")
@@ -78,6 +78,8 @@ func stmFunc(cmd *cobra.Command, args []string) {
 	}
 
 	switch stmIsolation {
+	case "c":
+		mkSTM = v3sync.NewSTMReadCommitted
 	case "r":
 		mkSTM = v3sync.NewSTMRepeatable
 	case "s":